Patent GB-648395-A (GB)
Title: Improvements in or relating to fibrous filter media
IPC: D01F2/28
Filed: 1947-09-23
Abstract: Filter media, suitable for filtering spinning solutions for the production of artificial filaments, are produced by impregnating a felted sheet of fibres with a solution of an adhesive which under the conditions employed in the making of the filter medium undergoes no substantial degree of chemical change, compressing the impregnated sheet of fibres and depositing the adhesive from the solution while the sheet of fibres is in the compressed state. For example, a felted sheet of cotton fibres may be impregnated with an aqueous solution of a water-soluble methyl cellulose and then compressed and the water evaporated.  Fibres of regenerated cellulose, cellulose acetate, a cellulose ester or ether, a polyvinyl compound, a polyamide, or other linear high polymer may be used, provided they are not attacked or dissolved by the liquid to be filtered.  The adhesive should also be resistant to the liquid to be filtered, and may comprise a cellulose acetate of moderate or fairly low acetyl value, for example 53-55 per cent, calculated as acetic acid.  The adhesive may be removable by the material being filtered.  For example, in assembling jets for spinning cellulose acetate filaments the filter for insertion behind the jet orifices may be cotton fibres impregnated with a 1-4 per cent solution of cellulose acetate in acetone and the acetone removed by evaporation.  The resulting filter medium can be manipulated without the separation of loose fibres, even though the cellulose acetate is subsequently washed out.ALSO:Filter media are produced by impregnating a felted sheet of fibres with a solution of an adhesive which under the conditions employed in making the filter medium undergoes no substantial degree of chemical change, compressing the impregnated sheet of fibres, and depositing the adhesive from the solution while the sheet of fibres is in the compressed state.  For example, a felted sheet of fibres, most or all of which exceed about 5/8 inch in length, the sheet being of initial thickness about 1/2 inch, may be impregnated with an aqueous solution of a water-soluble methyl cellulose and then compressed to a thickness of 1/10 inch or 1/25 inch and the water evaporated.  The solution concentration may be 1 to 5 per cent or more.  Fibres of regenerated cellulose, cellulose acetate, a cellulose ester or ether, a polyvinyl compound, a polyamide, or other linear high polymer may be used, provided they are not attacked or dissolved by the liquid to be filtered.  The adhesive should also be resistant to the liquid to be filtered, and may comprise a cellulose acetate of moderate or fairly low acetyl value, for example, 53-55 per cent calculated as acetic acid.  The adhesive may be removable by the material being filtered.  For example, in assembling jets for spinning cellulose acetate filament, the filter for insertion behind the jet orifices may be cotton fibres impregnated with a 1-4 per cent solution of cellulose acetate in acetone and the acetone removed by evaporation.  The resulting filter medium can be manipulated without the separation of loose fibres, even though the cellulose acetate is subsequently washed out.